1. Field of the Invention
The invention is directed to a press fitting for producing a permanent or nondetachable tight connection of smooth-ended pipes.
2. Discussion of the Prior Art
It is known (see brochure: Mannesmann Pre.beta.fitting GmbH, Release 8/1994) to produce a nondetachable tight connection of smooth-ended pipes with a fitting which engages around the smooth ends of the pipes and each of whose bead-shaped ends receives a sealing ring. The bead-shaped end and, at the same time, the adjacent cylindrical area of the fitting are deformed together with the pipe plastically and with the enclosed sealing ring elastically by means of an exchangeable holding device with articulated jaws which is connected with an actuating device. The sealing function of the connection is achieved in that the sealing ring is elastically deformed by the plastic deformation of the bead-shaped end of the press fitting and, along a defined portion of the cross-sectional circumference, linearly contacts the surrounding surface areas of the bead-shaped end of the fitting and of the pipe. In order to absorb the longitudinal forces occurring at a corresponding internal pressure, the cylindrical area of the fitting adjacent to the bead-shaped end is plastically deformed together with the pipe. Both the bead-shaped end and the adjacent cylindrical area are deformed simultaneously by means of the actuating device during pressing.
As a rule, a connection point that is not pressed leads to detectable leakage in the pressure test which must be carried out according to regulations following installation. However, in special cases, it may happen that the tolerance matching of the pipe and fitting is so unfavorable that, when the smooth-ended pipe is pushed in, the sealing ring undergoes a pre-deformation which, although only slight, is sufficient to withstand the pressure test during inspection of the installation. However, when the line breathes in subsequent operation, i.e., fast-switching valves lead to water hammers or pressure shocks, relative movements can come about depending on heating, so that, in the absence of axial securing when there is no pressing, the previously resulting slight pre-deformation of the sealing ring is not sufficient to further ensure the tightness of the connection point.